Automatic electronic load holder



.April 17, 1945. Y J. SNERTSN 2,373,788

AUTOMATIC ELECTRONIC LOAD HOLDER Filed March 26. 1941 3 Sheets-Sheet l ATTORNEY A Pll 17, 1945- J. slvERfrsEN 2,373,788

AUTQMATIC ELECTRONIC LOAD HIOLDER I Filed March 26, 1941 s sheets-sheet 2 l". J, .INVENT'OR s1 2% W mmfm ATTOREY v April 17, 1945@ .LslvER'rsEN 2,373,788

i R NIC LOAD HOLDER Filed March 26, 1941 'eff 1 Patented Apr. 17,1945

AUTOMATIC ELECTRONICLOAD HOLDER Jens Si've'rtsen, Philadelphia, Pa., assignor to `Tinius Olsen Testing Machine Company, Philadelpha, Pa., a corporationo'f Pennsylvania Application March 26, 1941,serial No. 385,386

s claims. (ci. 25o- 27) My invention relates to'testing. machines fon arrangement and organization of these instrul testing the physical properties of Inaterlala and involves a new method and apparatus for electronic control of testing machines or other types of machines.

In the art of testing materials; it is 'necessary in some cases to maintain a constant load, Withinl close limits, on the specimen for a long period of time, such as hours, days, weeks `and even months. Accuracy and reliability are necessary for such tests. An apparatus of' this kind consists primarily vof three parts.

A. An instrument to detect deviation from the prescribed load. B, Means to correct the deviation. C. Means whereby A, the .detecting means, can

affect B, the correcting means, to bring about the necessary correction.-

The detecting means and control means `can tectors can be used, such as photocells, capacity, inductance, or contacts together with relays, or

vacuum tubes can be used instead of relays.l

mentalities as herein set forth.

Figure 1 is a side elevation, partly in section, of any electronic load holder embodying my in vention. Figure 2is a top plan view of Figurexl. Figure 3 is a sectional planyiew,v the section being `taken on line 3-3 of Figure `l.

Figure lis va side elevation of a control valve employed.

Figure 5 is a 'sectional view of the valve plug,

on line 5-/5 of Figure 4.

l be hydraulic or electrical. Different kinds of deating valve.

points used to switch on and oil' the power which the relay controls. v .f

vln accordance with this inventioncontacts are not used to :break the flow of current.

With the foregoing and .otherobjects in v-vievv as will hereinafter clearly appear, my invention comprehends a novel hydraulic, electronic load holder.-

It further comprehends a novel electronic control, which, while particularly designed for the typical embodiment thereof, which in practice j will .give satisfactory and reliable results. It is', however, :to be understood that the -various instrumentlities of `which my invention consists can be variously' arranged' and organized, and that my invention is not limited to the exact dial indicator.

Similar numerals vof reference indicatecorre- Figure 6'is a sectional view of the valve plug. Figure '7 isaA sectional View of the valve casing. Figure 8 is a wiring diagram..

Figure 9 is a diagrammatic view of va testing machine and connections to the the electronic'control. FigurelO is adetail sponding parts.

Referring to the :drawings:

. As shown in Figure '9, I designates the cylinder of an hydraulic testing machine and 2 the piston. 3 is an oil reservoir.' 4 is a pump and 5 the oper,- G'is a releasevalve.'` 'I is 'anautomaticY pressure valve which holds -a constant, hydraulic potential difference between: the pressure side of: the pump and the cylinder of the testing machine.

/The load holder is vconnected to this substantially standard arrangement by pipes Sand 9, which communicate with a novel control valve I0. The control valve I0 has one end of a lever II connected with it, vthe other end of said lever being connected to a movable part of a solenoid I2 to cause the valve I|J .to turn when the solenoid is energized. I3 and I4 are manually actuated adjusting valves for the load holding apparatus. The' valve I0,Ysee more particularly Figures 4, 5,r 6 and 7, is-balanced,fand, due to the slight movement lof its valve plug I5, a long lever arm rvcarrbe used. The valve plug |'5 is accurately l construction, a nearly perfect polish can be given oil lm,`which further reduces friction.

total result of such valve arrangement is a sensito the valve plug and the bore of the valve casing Il.' This results in very little friction and very little wear, so that the valve mechanism will stand up for a very long time without undesired leakage, and, therefore, will'be reliable in operation.

The small clearance between the valve plug and the valve casing provides for the presence of an The control valve'of showing` the hands of the l tive valve that moves easily, considering the pressures involved, and one which has a minimum of wear.

The valve casing Il has an inlet I8 and an outlet I9 which are threaded to receive the pipes B and 9, respectively The valve plug has ports 29 and 2| which communicate with the passage 22. A passage 23 leads to opposite sides of the Valve plug to balance the pressures, and, in a similar manner, a passage 24 leads from the port I8 to opposite sides of the valve plug to balance the pressures on the plug. The valve plug is retained in assembled relation with its valve casing by the nuts 24 and 25. i

The movable part of the solenoid, see Figures 1 and 3, is retained in its lowered position by a spring rod 26, fixed at one end to the casing 21,'y

and having its free end bearing against a pin 28 fixed to the lever I I.

Referring now more particularly to the wiring diagram seen in Figure 8, I have shown an electronic control, employing a power transformer 29, the solenoid I2, power tubes 30, a control tube 3 I, a relay 32 and resistors 33, 34, 35 and 36. The other resistors and condensers are arranged and used in a conventional manner.

The relay 32 is a standard D. C. relay of the double pole, double throw type, with a large number of turns on the coil for a small current and a high voltage.

The resistor 33 is of very high ordenfty to one hundred million ohms. vFor certain arrangements where short leads can be used in the control circuit, it can be greater than that above stated, and when high sensitivity is not required it can be lower.

The resistor 34 can be two million ohms, more or less, depending on the characteristics of the tube 3|, the size of resistor 33, and the voltage of transformer 29.

-The tubes 39 should be power tubes, and, as illustrated, theyy are class A tubes. Class A tubes are tubes which will pass a large amount of current when their grids are at the same potential as the cathodes (or filaments).

The cable 31 is adapted to be connected with a source of supply of 110 volt, 60 cycle current and with a switch 38, which is connected by lines 39 and 40 with the primary windings of the transformer 29 to complete the primary circuit of the transformer.

4 is a heater winding to heat the laments of the power tubes 30. The heater winding 42 heats the filament of the tube 3|. The third secondary winding 43 of the transformer 29 is center tapped at 44. This winding 43, is a high voltage winding, approximately one thousand volts, and supplies power through the tubes-30 tov operate the solenoid I 2 and the valve II),l as herein described. This winding 43 also supplies power to operate the coil 45 of the relay 32, by tube 3|. The transformer also supplies the control current for the pointers of the indicator, by means of resistors 33 and 34, and the current for the' resistors 35 and 36. Assuming now that the primary circuit for lthe transformer is completed, and the heater filaments of the tubes are heated by their windings, the resistors 33 and 34 will bias the grid of the tube 3|, so that this tube will substantially not pass any plate current, even though the plate is supplied with plate voltage from 46 of the high voltage winding of the transformer. When the lower limit pointer 41, wired to point 48, touches the indicating pointer 49, the resistor 34 is shorted to ground. The point 50 will then be at zero potential, while it previously had a potential opposite to that of point 46. The tube 3| will now pass plate current from point 46 to resistor 5I, relay coil, plate of tube 3| and from plate to cathode of tube 3| and to ground, which is the same as thecenter point of the secondary winding. This operates relay 32, and the movable con* tacts 52 and 53 will change their position from the upper to the lower contacts of the relay. Previous to this, the tubes 30 did not pass current, although they had plate voltage, due to the fact that they were biased by resistors 35 and 36 to have a grid bias opposite to that of the plate Voltage.

The operation of the relay connects the grids with the filaments 'of the tubes 39, from winding 4|, and the grids will have substantially the same A. C. potential as the cathodes of the tubes 30.

This allows the tubes 30 to pass current, and they will act as a full rectifier supplying D. C. current to the solenoid. i

Since each tube 3D acts alike, we will refer only to the lower tube 30. I

When the'point 46` is positive, we obtain a current throughthe plate, the filament of the tube, winding 4I, solenoid l2, resistor 54, and pilot light 55 to groundpwhich is the center tap 44 of the secondary winding. The pilot light, when lighted, indicates that the circuit is in operation.

The energization of the solenoid, draws upwardly the lever II, loading spring 26 and turns valve plug I5 into position for the ports 2|! and 2| to register with I3 and I9 .respectively This causes oil to pass from the pump 4, by pipe 8, Valve I4, valve I3, pipe 9, and Valve I3 into the cylinder I of the testing machine. This will cause the load indicating pointer to rise and break the contact between the two pointers. The tube 3| will cease to pass'currenh'the relay coil will be de-energized, the movable contacts of the relay will change their position, and the tubes 33 will cease to pass current. The spring 26 now brings the valve plug into a position to cause ports 20 and'ZI to be out of registry with I8 and I9 respectively. When the indicator pointer falls oif, due to leakage in thel cylinder or for any other reason, and again touches the lower limit pointer, the cycle is repeated.

When the solenoid is energized the pilot light is lit, and when the solenoid is deenergized, the

pilot light is extinguished.

A cover 56 is provided to protect the electronic control.

The load indicating pointer 49 of the testing machine is grounded to the frame by a metallic connection, and the'lower limit pointer 41 is insulated from the frame of the machine. The Aarrangement is such that when the load on the specimen diminishes to the lower limit, contact is made between 'the two pointers, which acts as a shorting of the resistor 34 to ground. A. C. current will pass throughthe contacts, but the amount will be very small and not sufiicient to injure the contacts, evenafter a long usage, due to the fact that this current is connected in series with a resistor 33 of very high magnitude. The voltage trying to establish the contact if the ground is not perfect is quite high, and results in a very satisfactory arrangement, which will be clearly understood from the following:

Let us assume that half of the secondary ofthe transformer 29 is 520 volts i. e. between ground (the center of the secondary windings) and the end where resistor 3| is connected, and that resistor 33 is 50 megohms and resistor 34 is two megohms.

, current. n y voltage disappears, `as the grids are broughttor The current ycan be readily replaced due to their low cost after Before contact is made between the load indicatingpointer 41 and the lower limit pointer `49,

there will be approximately volts acrossfthe contacts, which is considerable voltage to ensure contact. The current, however, when contact is established, is .very small, approximately 10 microamps. When the contact again breaks, there will not be any sticking or arcing due to the small having served for a specified number of hours, ir-

f respective Vof their condition.

Having thus described myv invention, what I claim as new and desire to secure by Letters Patent is:

v 1. An electronic control system to maintain a predetermined, constant load on a testing machine, comprising a power transformer with an alternating current supply to its primary, and with a high voltage secondary, resistors across said high voltage secondary, two power tubes supplied with an alternating current voltage through grid voltage and the plate voltage of tube 3l are exactly 180 degrees out of phase. This will block current passing from plate to cathode of the tube, thereby, also through the coil of the relay.

As soon as the contact arrangement shortens resistor 34, the tube 3| passes current in the platecathode path and the D. C. relayf32 becomes energized. This throws the contacts of the relay over for the grid connections of the tubes 30. These tubes are arranged in asimilar way, with the plate and the grid voltage 1'80 degrees out of phase, and are thereby prevented from passing When the relay is energized, the grid the same potential as the cathode. in the plate circuit will rise and energize the solenoid l2, and this will cause the valve `Il) to' open and apply load to the specimen in the testing mav chine.' The pointers will break the contact and the valve l0 closes.

If we assume that the current in the solenoid is 250 milliamps and the remaining voltage, plate to cathode,.is approximately 100 voltsgi. e. 400 volts across the load (solenoid I2), we obtain a delivered wattage in the solenoid of .25 times 400 equals 100 watts. l

The amount to-be dissipated inthe two tubes, however, willbe only l5 watts per tube, `which is reasonable.` f

The control ratio will be:

lOO watts in the solenoid '10 4 Watts fOITWgLOOOOOto l We are able to control an energy a 'million times greater than the input, with-very simple means. n Onefeature is thatthe arrangement does not have any contacts to breaky or contacts to burn in the relay, and the arrangement `will work indefinitely in service.

' The tubes, as today manufactured, are very reliable and as a rule lose power gradually, They said resistors from said high voltage secondary, a control tube and a relay, said relay controlled by the control tube havingv two sets of xed and movable contacts, with the movable contacts connected to the grids of saidpower tubes, the fixed contacts being connected to said resistors to cause the plate voltages and the grid voltages of saidpower tubes to counteract each othery when the relay is not energized, the energization of said' relay causing the 'grid voltage to become substantially the samel as the cathode voltage of said power tubes to cause said power tubes t0 pass a substantial amount of current for the desired control.l l

2. Av control system comprising a transformer; l an impedance shunted across the secondary of the transformer, a power tube having a plate, a grid and a cathode, a relay havingv a movable contact and two stationary contacts, a primary con-v trol tube to energize said relay, said movable contact being connected to the grid of the power tube, the plate of the power tube beingconnected to one of the terminals of the secondary, the cathodel of the power tube being connected to a tap on said secondary, one of the stationary cony.tacts -being connected to said impedance, the

other stationary contact being connected'with the cathode of said power tubek to cause current to be passed by the power tube upon the energization of said relay by said control tube.

3. AA control system, comprising a transformer, an impedance shunted across the secondary of the transformer, two power tubes, each having plate, gri-d and cathode, a relayhaving two sets of movable and stationaryA contacts, a primary control tube to renergize said relay, the movable contacts being connected to the grids of the powerr tubes, they plates of the power tubes being connected to opposite terminals of the secondary, the cathodes of the power tubes being connected together and over a load impedance to the'center of the secondary, one of the stationary contacts of each lset being connected to opposite points on the impedance, the othertwo stationary contacts being 'connected together and to the 'cathodes to cause current to be passed by the power tubes on energization of said relay by said control tube.

JENs sIvERTsEN. 

